From 1917eafa8c0d4fbf9a3fc2d61955652d26dd756e Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 11 Jun 2020 19:04:21 +0100
Subject: drm/i915: Leave vma intact as they are discarded
Git-commit: 51dc276dd2af20ae9468afbd864fa8b0e1c75827
Patch-mainline: v5.9-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

If we find ourselves trying to reuse a misplaced but active vma, we
currently try to discard it to avoid having to wait to unbind it
(upsetting the current user fo the vma). An alternative to marking it as
a dicarded vma and keeping it in both the obj->vma.list and
obj->vma.tree, is to simply remove it from the lookup rbtree.

While it remains in the list of vma, it will be unbound under eviction
pressure and freed along with the object. We will never reuse it again
for new instances. As before, with no pruning, the list may continually
grow, but eventually we will have the most constrained version of the
ggtt view that meets all requirements -- so the list of vma should not
grow without bound.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2012
Fixes: 9bdcaa5e3a2f ("drm/i915: Discard a misplaced GGTT vma")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200611180421.23262-1-chris@chris-wilson.co.uk
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/i915/i915_gem.c | 38 +++++----------------------------
 drivers/gpu/drm/i915/i915_vma.c |  3 ++-
 2 files changed, 7 insertions(+), 34 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 41553e9e57a9..9aa3066cb75d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -933,44 +933,16 @@ void i915_gem_runtime_suspend(struct drm_i915_private *i915)
 	}
 }
 
-static bool
-discard_ggtt_vma(struct i915_vma *vma, const struct i915_ggtt_view *view)
+static void discard_ggtt_vma(struct i915_vma *vma)
 {
-	const struct i915_ggtt_view discard = {
-		.type = I915_GGTT_VIEW_PARTIAL,
-	};
 	struct drm_i915_gem_object *obj = vma->obj;
 
 	spin_lock(&obj->vma.lock);
-	if (i915_vma_compare(vma, vma->vm, &discard)) {
-		struct rb_node *rb, **p;
-
+	if (!RB_EMPTY_NODE(&vma->obj_node)) {
 		rb_erase(&vma->obj_node, &obj->vma.tree);
-		vma->ggtt_view = discard;
-		GEM_BUG_ON(i915_vma_compare(vma, vma->vm, &discard));
-		GEM_BUG_ON(i915_vma_compare(vma, vma->vm, view) == 0);
-
-		rb = NULL;
-		p = &obj->vma.tree.rb_node;
-		while (*p) {
-			struct i915_vma *pos;
-			long cmp;
-
-			rb = *p;
-			pos = rb_entry(rb, struct i915_vma, obj_node);
-
-			cmp = i915_vma_compare(pos, vma->vm, &discard);
-			if (cmp < 0)
-				p = &rb->rb_right;
-			else
-				p = &rb->rb_left;
-		}
-		rb_link_node(&vma->obj_node, rb, p);
-		rb_insert_color(&vma->obj_node, &obj->vma.tree);
+		RB_CLEAR_NODE(&vma->obj_node);
 	}
 	spin_unlock(&obj->vma.lock);
-
-	return i915_vma_compare(vma, vma->vm, view);
 }
 
 struct i915_vma *
@@ -1035,8 +1007,8 @@ i915_gem_object_ggtt_pin(struct drm_i915_gem_object *obj,
 		}
 
 		if (i915_vma_is_pinned(vma) || i915_vma_is_active(vma)) {
-			if (discard_ggtt_vma(vma, view))
-				goto new_vma;
+			discard_ggtt_vma(vma);
+			goto new_vma;
 		}
 
 		ret = i915_vma_unbind(vma);
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 2a0eb3c36e47..f4e22e256ac6 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1084,7 +1084,8 @@ void i915_vma_release(struct kref *ref)
 
 		spin_lock(&obj->vma.lock);
 		list_del(&vma->obj_link);
-		rb_erase(&vma->obj_node, &obj->vma.tree);
+		if (!RB_EMPTY_NODE(&vma->obj_node))
+			rb_erase(&vma->obj_node, &obj->vma.tree);
 		spin_unlock(&obj->vma.lock);
 	}
 
-- 
2.29.2